Hi,
I see same issue with default protostar template. In" show_block_login" file I see this:
$this->checkoutHelper->displayMessages('login');
and for login messages are showing fine, they displayed like this:
<div class="alert alert-warning alert-block"><button type="button" class="close" data-dismiss="alert">×</button><p>Username and password do not match or you do not have an account yet.</p></div>
but for registration or guest the "alert-warning" class is missing.
I have checked Joomla from where this message comes and all seems fine. I also have tried to register via joomla registration and error was showing fine. Except that different language string was in use.
Is there anything more could be checked?
Seems that type of error message is not defined.
Thanks